<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
  <style>
    *{
      margin: 0;
      padding: 0;
    }
    #main{
      display: flex;

    }
    #left{
      width: 200px;
      height: 200px;
      background: red;
    }
    #center{
      flex: 1;
      height: 300px;
      background: green;
    }
    #right{
      width: 200px;
      height: 200px;
      background: blue;

    }
  </style>
</head>
<body>
<div id="main">
  <div id="left"></div>
  <div id="center"></div>
  <div id="right"></div>
</div>

</body>
</html>